Evaluated Cross Sections of Photoneutron Reactions on the Isotope 116 Sn and Spectra of Neutrons Originating from These
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CLEI Theory
Evaluated Cross Sections of Photoneutron Reactions on the Isotope 116 Sn and Spectra of Neutrons Originating from These Reactions V. V. Varlamov1)* , B. S. Ishkhanov1), 2) , and V. N. Orlin1) Received May 24, 2017
Abstract—With the aid of the results obtained by evaluating cross sections of partial photoneutron reactions on the isotope 116 Sn and the energy spectra of neutrons originating from these reactions, the possible reasons for the well-known discrepancies between the results of different photonuclear experiments were studied on the basis of a combined model of photonuclear reactions. On the basis of physical criteria of data reliability and an experimental–theoretical method for evaluating cross sections of partial reactions, it was found that these discrepancies were due to unreliably redistributing neutrons between (γ, 1n), (γ, 2n), and (γ, 3n) reactions because of nontrivial correlations between the experimentally measured energy of neutrons and their multiplicity. DOI: 10.1134/S1063778817060230
1. INTRODUCTION
σdω ≈ 60
Investigation of the mechanism of photon interaction with nuclei is one of the priority lines of research in nuclear physics. A feature peculiar to photon interaction with nuclei is their intense absorption in the energy range between 8 and 20 MeV—a giant dipole resonance (GDR). The GDR phenomenon is observed in all nuclei, without exception. For the first time, it was predicted by A.B. Migdal [1] and was experimentally observed by Baldwin and Klaiber in 238 U photofission [2] and in photoneutron reactions on the isotopes 12 С and 63 Cu [3]. In collective models of the nucleus, the giant dipole resonance is interpreted as the vibration of all intranuclear protons with respect to all intranuclear neutrons in photon absorption by the nucleus being considered [4]. Within the collective models, it turned out to be possible to relate GDR properties to fundamental properties of the nucleus such as its radius and mass and the numbers of neutrons, N , and protons, Z, in it. In particular, the resonance-maximum position Em and the total cross section of photon interaction with the nucleus depend on the number of nucleons, A, in the nucleus, A = N + Z; that is, Em = hω ≈ 78A−1/3 [MeV], 1)
(1)
Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119991 Russia. 2) Faculty of Physics, Moscow State University, Moscow, 119991 Russia. * E-mail: [email protected]
NZ [MeV mb]. A
(2)
GDR
The prediction and subsequent discovery of splitting of the maximum of the giant resonance in deformed nuclei that corresponds to nuclear-matter vibrations along the axes of the nuclear ellipsoid [5, 6] were undoubtedly a success of collective models. The advent of the shell model made it possible to interpret GDR states as photon-induced nucleon transitions from occupied to unoccupied nuclear shells. For the first time, such an interpretation was proposed by Wilkinson [7]. However, the resonancemaximum position determined theoretically in his study proved to be lower on the
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